Note: Descriptions are shown in the official language in which they were submitted.
CA 02496056 2005-02-04
IGNITION SYSTEMS FOR PORTABLE POWER TOOLS
BACKGROUND OF THE INVENTION
[0001 ] The present invention relates, generally, to ignition systems for
portable power tools and, in particular, to ignition systems that include an
ignition
switch, choke mechanism and air filter unit.
[0002] Portable power tools such as chain saws, hedge trimmers, edgers
and blowers, typically, are powered by a gasoline engine the operation of
which is
controlled by an ignition switch: The ignition switch is manually movable
between
an "On" position allowing the engine to operate and an "Off' position
preventing the
engine from operating. Usually, these power tools are also provided with a
manually controlled choke mechanism to facilitate the starting and running of
the
gasoline engine. The engine requires both fuel and air to operate and, by
manipulating the choke mechanism, the relative quantities of air and fuel
delivered
to the engine are varied so that the engine can be readily started and,
thereafter,
operated. For example, if the engine has been idle for a period of time and
the
ambient temperature is relatively low, in order to start the engine, it is
necessary
that an air-fuel mixture that is rich in fuel be delivered to the engine with
the ignition
switch in the "On" position. To produce a fuel-rich air-fuel mixture the choke
mechanism is adjusted so that it restricts the intake of air to the engine.
Once the
engine has started, the choke mechanism is adjusted once again so that the
quantity of air, in relation to the quantity of fuel delivered to the engine,
is increased
until a ratio of air to fuel is attained that allows for optimum operation of
the engine.
At such time as it is desired to discontinue operating the power tool, the
ignition
switch is moved to the "Off' position.
[0003] The air and fuel are mixed in the engine's carburetor before being
delivered to the engine and, typically, the choke mechanism controls the
position of
a valve in the flow path of the air to the carburetor so as to control the
quantity of air
entering the carburetor. Because it is important to the efficient operation of
the
engine that the air be as free of particulate matter as possible, the air is
passed
through an air filter unit before it is introduced into the carburetor.
CA 02496056 2005-02-04
SUMMARY OF THE INVENTION
[0004] From the foregoing it will be understood that there is a cooperative
operational relationship among the ignition switch, the choke mechanism and
the
filter unit, as incorporated into and applied to the portable power tool and
the
present invention affords certain improvements in that operational
relationship.
Thus, according to the present invention, an air filter unit is provided on
which the
ignition switch is mounted. Additionally, the ignition switch and choke
mechanism
are arranged in a coactive relationship wherein the ignition switch and a
choke lever
in the choke mechanism are located adjacent one another and have engaging
parts
such that the ignition switch will be moved to an "On" position by the choke
lever
when the choke lever is moved to a position where it has reduced the air flow
to the
carburetor and caused the air-fuel mixture delivered to the engine to become
fuel-
rich. Also, the present invention provides for the integration of the coactive
ignition
switch and choke mechanism with the filter unit.
[0005] According to one aspect, the filter unit comprises a housing for
holding an air filter, the housing having a port in communication with an
inlet port in
the carburetor for the passage of air from the housing to the carburetor.
Means are
included on the housing by which the housing may be secured to the portable
power
tool. Also included on the housing is a mounting element for the mounting
thereon
of the ignition switch for the portable power tool.
[0006] According to another aspect, the housing for holding the air filter
includes a housing base and a housing cover for the housing base. The housing
base includes a housing base floor that has ports through which air flows to
the
carburetor. The housing base floor also has means by which the housing base
may
be attached to the carburetor of the power tool. A housing base perimeter wall
is
integral with the housing base floor and extends, generally, perpendicularly
from the
perimeter of the housing base floor in the direction of the housing cover. The
housing base perimeter wall has an inside surface and an outside surface, and
the
inside surface of the housing base perimeter wall and the housing base floor
define
a housing base interior. The housing base perimeter wall includes an anterior
section, a posterior section, a first lateral section joining one terminus of
the anterior
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section to one terminus of the posterior section and a second lateral section
joining
the other terminus of the anterior section to the other terminus of the
posterior
section such that the housing base perimeter wall, when the housing is
installed in
the portable power tool, has its anterior section nearest the front of the
power tool,
its posterior section nearest the rear of the power tool and its first and
second lateral
sections disposed toward opposite sides of the power tool. Integral with the
first
lateral section of the housing base perimeter wall is an augmentation that
extends,
substantially, perpendicularly from the housing base floor in a direction away
from
the housing cover. A pair of opposed support legs for securing the housing
base to
the chassis of the portable power tool are provided. A first of the opposed
support
legs is integral with the augmentation and the second of the opposed support
legs is
integral with the second lateral section of the housing base wall. A mounting
element integral with the outside surFace of the first lateral section of the
housing
base perimeter wall is provided for the mounting thereon of the ignition
switch for
the portable power tool.
[0007) According to yet another aspect, an ignition assembly for a portable
power tool having a carburetor and an ignition circuit is provided. The
assembly
includes a choke lever connected to an air valve for controlling the flow of
air to the
carburetor. The choke lever is reciprocally movable between a first position
in
which air flow to the carburetor of the portable power tool is not
substantially
restricted and a second position in which air flow to the carburetor is
substantially
restricted. The choke lever includes a depending abutment. An ignition switch
is
positioned on a mounting element in the portable power tool so as to be
movable
between an "On", or run, position in which the power tool may be operated, and
an
"Off', or stop, position in which the power tool may not be operated. The
ignition
switch includes a depending abutment located in the line of reciprocal
movement of
the depending abutment of the choke lever when the ignition switch is in the
stop
position so that reciprocal movement of the choke lever from its first
position to its
second position causes the depending abutment on the choke lever to engage the
depending abutment on the ignition switch and move the ignition switch from
the
stop position to the run position. The assembly also includes a leaf spring
that
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engages the ignition switch at a first site of engagement on the ignition
switch when
the ignition switch is in the stop position and at a second site of engagement
on the
ignition switch when the ignition switch is in the run position. The leaf
spring is
biased for alternatively applying a force to the ignition switch at the first
and second
sites of engagement in a direction toward the mounting element and away from
the
choke lever.
[0008] According to further aspects, the ignition assembly as described
above includes, separately or in combination, the following features: The
ignition
switch is positioned on the mounting element for pivotal movement between the
run
position and the stop position. The leaf spring is, generally, S-shaped and
has an
intermediate section, a first terminal section connected to one end of the
intermediate section of the leaf spring and a second terminal section
connected to
the other end of the intermediate section of the leaf spring. The leaf spring
is held
in place on the power tool at the intermediate section and the first terminal
section
of the leaf spring alternatively engages the ignition switch at the first and
second
sites of engagement on the ignition switch as the ignition switch is moved
between
the stop position and the run position. The leaf spring forms a part of the
ignition
circuit, and the continuity of the ignition circuit is established when the
first terminal
section of the leaf spring engages the ignition switch at the first site of
engagement
and the continuity of the ignition circuit is interrupted when the first
terminal section
of the leaf spring engages the ignition switch at the second site of
engagement. The
second terminal section of the leaf spring is connected to the ignition
circuit and the
ignition switch includes an electrical conductor located at the first site of
engagement on the ignition switch and also connected to the ignition circuit.
The
first terminal section of the leaf spring includes a rounded protuberance that
alternately engages the ignition switch at the first and second sites of
engagement.
The ignition switch includes a, substantially, circular opening and the
electrical
conductor comprises an annulus that is press-fitted in the substantially
circular
opening. Positioning means are located adjacent the substantially circular
opening
in the ignition switch for maintaining the electrical conductor in place in
the
substantially circular opening in the ignition switch.
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[0009] According to still another aspect, the ignition assembly, as described
above, is brought together and integrated with the filter unit, by mounting
the ignition
switch of the ignition assembly on the mounting element located on the filter
housing
base of the filter unit.
(0010] According to yet other aspects, the mounting element comprises a,
generally, cylindrical projection and the ignition switch is mounted for
pivotal
movement on the cylindrical projection between a position placing the power
tool in
an "Off', or non-operating, mode and a position placing the tool in an "On",
or
operating mode. The housing includes a stop lug adjacent the cylindrical
projection
for limiting the pivotal movement of the ignition switch beyond the position
placing
the power tool in an operating mode and a guide lug adjacent the stop lug for
providing a guiding surface for the choke fever. A pair of positioning
elements are
included on the filter housing adjacent the mounting element, the positioning
elements being separated from one another so as to establish a space into
which
may be positioned the intermediate section of the S-shaped leaf spring. Each
positioning element has an engaging surface adapted to engage the S-shaped
leaf
spring at a respective location at which the intermediate section of the S-
shaped
leaf spring is joined to a terminal section of the S-shaped leaf spring.
[0011] According to an additional aspect, the air filter housing cover rests
on
the air filter housing base and the air filter housing cover includes a
depending
portion that extends downwardly over the housing base so as to protect
electrical
wiring components connected to the terminal sections of the leaf spring. In
the case
where the housing base includes a housing base floor and anterior and first
and
second lateral perimeter wall sections, the depending section extends
downwardly
over the anterior section of the housing base perimeter wall where the
anterior
section is joined to the first lateral section of the housing base perimeter
wall and
beyond the housing base floor.
[0012] According to yet another aspect, access holes are provided through a
support leg for the air filter housing to provide access to the needles on the
carburetor.
CA 02496056 2005-02-04
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The foregoing and other features of the present invention will be
apparent from the description below with reference to the drawings wherein:
[0014] FIG. 1 is a side view of a chain saw incorporating the present
invention;
[0015] FIG. 2 is a perspective view of the invention with a portion of the
filter
housing cover broken away to illustrate the filter;
[0016] FIG. 3 is an exploded view of the invention;
[0017] FIG. 4 is a side view of the invention shown mounted to the chain saw
chassis and with the chassis and filter housing cover shown in cross section;
[0018] FIG. 5 is a side view of the invention shown mounted to the chain saw
chassis, with the chassis and filter housing cover shown in cross section and
with a
portion of the ignition switch broken away to illustrate the arrangements of
certain
parts of the invention when the ignition system is in an "Off' position; and
[0019] FIG. 6 is a side view of the invention shown mounted to the chain saw
chassis, with the chassis and filter housing cover shown in cross section and
with a
portion of the ignition switch broken away to illustrate the arrangements of
certain
parts of the invention when the ignition system is in an "On" position.
DETAILED DESCRIPTION OF THE INVENTION
[0020] FIG. 1 illustrates the invention, indicated generally at 10,
incorporated
into a chain saw indicated generally at 1. Although the invention is described
in
detail herein as used with a chain saw it may be applied to other types of
power
tools, including portable power tools such as, for example, hedge trimmers,
edgers
and blowers. As shown in FIG. 1, the invention is located within the confines
of the
outer cover 2 of the chain saw.
(0021] In general, the invention relates to an ignition system that includes
an
ignition switch, a choke mechanism and a filter unit. The ignition switch
includes a
lever 20 and the choke mechanism includes a lever 30, both of which extend
outside
the outer cover 2 of the chain saw. The levers 20 and 30 are provided to
enable the
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CA 02496056 2005-02-04
operator of the chain saw to readily manipulate the ignition switch and the
choke
mechanism, respectively, and both levers are positioned near the handle 3 of
the
chain saw for easy access by the operator.
[0022] The filter unit of the ignition system of the invention is best
described
with reference to FIGS. 2 and 3 of the drawings. As illustrated in these
figures, the
filter unit includes a filter housing, indicated generally at 40, and a filter
43 disposed
within the housing. The filter housing comprises a filter housing base,
indicated
generally at 41, and a filter housing cover 42. The filter housing and the
filter cover
can be made of any of a variety of suitable materials such as, for example,
metals,
heat-resistant composites or plastics. In the presently described embodiment,
the
filter housing base 41 and filter housing cover 42 are made of a hardened
plastic
and are configured so that the cover can be both snapped tightly onto the
housing
base and unsnapped from the housing base in a manner that is familiar to those
having ordinary skill in the art.
[0023] The filter housing base 41 includes a filter housing base floor 44 and
a filter housing base perimeter wall 45. The base floor 44 includes ports 46
and 47
that are in fluid communication with inlet ports in the chain saw carburetor
(not
shown) whereby air entering the filter housing through opening 42 A in the
filter
housing cover 42 and passing through filter 43 is drawn into the carburetor.
Air
entering the carburetor through port 47 mixes with fuel injected into the
carburetor
and the air-fuel mixture is delivered to the chain saw's engine where
combustion of
the fuel takes place. Air entering the carburetor through port 46 does not mix
with
fuel and is, simply, directed to the engine where it contributes to the
combustion of
the air-fuel mixture delivered to the engine. The arrangement of the
carburetor with
the engine and the manner in which the engine drive shaft drives the chain saw
blade 4 are, essentially, independent of the present invention and,
consequently,
are not described here. Various methods and designs for performing these
functions are well known to those skilled in the art.
[0024] The filter housing base floor 44 also is provided with several openings
48 through which the threaded portions, but not the heads, of the fasteners 49
can
pass. The fasteners are screwed into complementary threaded holes in the
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carburetor, and this arrangement constitutes the means by which the filter
housing
base 41 is attached to the carburetor.
[0025] The filter housing base perimeter wall 45 is integral with the housing
base floor 44 and extends, generally, perpendicularly from the perimeter of
the
housing base floor in the direction of the filter housing cover 42. As is best
seen in
FIG. 3, the housing base perimeter wall has an inside surface and an outside
surface with the inside surface of the perimeter wall and the housing base
floor 44
defining a housing base interior.
[0026] The housing base perimeter wall includes an anterior section 50, a
posterior section 51, a first lateral section 52 and a second lateral section
53. The
first lateral section 52 joins one terminus of the anterior section 50 to one
terminus
of the posterior section 51, and the second lateral section 53 joins the other
terminus of the anterior section 50 to the other terminus of the posterior
section 51.
Consequently, when installed in the chain saw, the anterior section is nearest
the
front 5 of the chain saw, the posterior section is nearest the rear 6 of the
chain saw
and the first and second lateral sections are disposed toward opposite sides
of the
chain saw.
[0027] In the embodiment of the invention shown in the drawings, the portion
54 of the first lateral section 52 of the filter housing base perimeter wall
that is
adjacent the posterior section 51 of the perimeter wall is recessed inwardly
toward
the housing base interior. Integral with the first lateral section 52 of the
housing
base perimeter wall is an augmentation, or extension, 55 that extends,
substantially,
perpendicularly from the filter housing base floor 44 in a direction away from
the
housing base cover 42. Further, the augmentation 55 and the recessed portion
54
of the first lateral section of the housing base perimeter wall are located in
substantially the same plane as can best be seen in FIGS. 2 and 3. Although
the
embodiment of the invention illustrated in the drawings includes a recessed
portion
54 on the first lateral section 52 of the housing base perimeter wall, it is
not
essential that the first lateral section be recessed.
(0028] The filter unit additionally includes a pair of opposed support legs
that
are positioned on the housing base 41. The first opposed support leg 56, as
shown
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in FIGS. 2 and 3, is integral with the augmentation 55. The second of the
opposed
support legs is structurally, essentially, the same as the first of the
opposed support
legs, is integral with the second lateral section 53 of the housing base
perimeter wall
and is located on the second lateral section 53 directly opposite support leg
56.
The opposed support legs secure the filter housing base to the chassis of the
chain
saw, with the cooperation of suitable fasteners, as shown in FIGS. 4,5 and 6
and,
thus, comprise a means on the filter housing by which the housing may be
secured
to the chain saw.
[0029] First opposed support leg 56 includes a pair of openings 57 that
extend through the leg and the augmentation 55 with which the leg is integral.
The
openings are aligned with the needles of the carburetor and, thus, provide
access
holes to the needles for the purpose of adjusting the carburetor.
[0030] The filter housing base also includes a mounting element for the
mounting thereon of the ignition switch for the chain saw. Specifically, the
mounting
element 58 is integral with the outside surface of the first lateral section
52 of the
housing base perimeter wall. As shown in the embodiment of the invention
illustrated in the drawings, the mounting element 58 is located on the
recessed
portion 54 of the first lateral section of the housing base perimeter wall.
[0031] The mounting element 58 comprises a, generally, cylindrical
projection that extends, generally, perpendicularly from the first lateral
section of the
filter housing base perimeter wall outwardly of the housing base interior. The
ignition switch, indicated generally at 29, includes a, generally, cylindrical
opening
21 that extends through the switch. The opening 21 is congruent with the
cylindrical
mounting element 58 and provides the means by which the ignition switch is
mounted on the mounting element for pivotal movement between a position
placing
the chain saw in a non-operating mode, i.e., the "Off' position, as
illustrated in FIG.
5, and an operating mode, i.e., the "On" position, as illustrated in FIG. 6.
The
ignition switch 29 is secured to the mounting element 58 by the fastener 61
with the
fastener being threaded into the threaded axial hole 59 in the mounting
element.
The fastener is not driven into axial hole 59 far enough to interfere with the
pivotal
movement of the ignition switch 29 on the mounting element 58.
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[0032] To assist in preventing the ignition switch 29 from proceeding in its
pivotal movement beyond the "On" position as shown in Fig. 5, a stop lug 60 is
provided on the fitter housing adjacent the cylindrical projection 58. As
shown in the
embodiment illustrated in the drawings, the stop lug is integral with the
outer surface
of the first lateral section 52 of the filter housing perimeter wall,
specifically the
recessed portion 54 of the first lateral section 52, and is located between
the
cylindrical projection 58 and the posterior section 51 of the housing base
perimeter
wall. As best shown in FIGS. 4 and 6, the arm 22 of the ignition switch
engages the
stop lug 60 to prevent the ignition switch from moving beyond the "On"
position.
[0033] The filter housing also includes a guide lug 62 adjacent the stop lug
60 for providing a guiding surface for the choke lever 30. As shown in the
embodiment illustrated in the drawings, the guide lug 62 is integral with the
outer
section of the first lateral section 52 of the filter housing base perimeter
wall,
specifically the recessed portion of the first lateral section, and is located
between
the stop lug 60 and the posterior section 51 of the housing base perimeter
wall. The
lever arm 31 of the choke lever 30, as the choke lever is pulled outwardly of
the
chain saw from the "Off' position shown in FIG. 5 to the "On" position shown
in FIG.
6, will tend to be guided along the guide lug 62.
[0034] Also included on the filter housing is a pair of positioning elements
63
located, generally, adjacent the mounting element 58. In the embodiment of the
invention illustrated in the drawings, the positioning elements are integral
with the
augmentation 55 and are located forwardly of the mounting element 58. The
positioning elements are separated from one another so as to establish a space
64
in which is located the intermediate section 65 of an S-shaped leaf spring.
Joined to
each end of the intermediate section of the leaf spring is a first terminal
section 66
and second terminal section 66A of the leaf spring, respectively. Each
positioning
element has an engaging surface 67 that engages the S-shaped leaf spring at a
respective location at which the intermediate section 65 of the S-shaped leaf
spring
is joined to a terminal section 66 and 66A of the S-shaped leaf spring.
[0035] The foregoing description is directed, largely, to the structure of the
air filter housing and to the interrelationship between the housing and the
ignition
CA 02496056 2005-02-04
switch and the choke lever. What follows is a more detailed description of the
ignition switch and the choke lever and the manner in which the ignition
switch and
the choke mechanism, including the choke lever, function, particularly as they
function in cooperation with the filter housing of the invention.
[0036] The choke lever of the choke mechanism and the ignition switch
function cooperatively as an ignition assembly for the chain saw in
conjunction with
a chain saw ignition circuit. The operation of an ignition circuit of a power
tool such
as a chain saw is well known to those skilled in the art. In general, the
ignition circuit
includes an ignition module that develops electrical current pulses in
response to
the rotation of a permanent magnet past the ignition module. Typically, the
magnet
is mounted on a flywheel that is caused to operate by an operator pulling on a
rope
starter attached to the flywheel. The current pulses are transmitted to a
spark plug
that generates sparks in response to the current pulses. The sparks, in turn,
ignite
the air-fuel mixture that has been delivered to the engine of the chain saw by
the
carburetor. The ignition module is connected by ground wires to the engine and
by
a lead wire to the ignition switch, as will be more fully described below. It
may be
noted here, however, that when the ignition switch is in the "Off' position,
the
ignition module is grounded and does not provide current pulses to the spark
plug.
On the other hand, when the ignition switch is in the "On" position the
ignition switch
is not grounded and is able to deliver current pulses to the spark plug.
[0037] With reference to the drawings, it can be seen that the chain saw is
provided with a choke mechanism that includes the choke lever 30 and a valve
lever
indicated, generally, at 68. The valve lever includes an arm 69, provided with
a hole
71, and a rod 70. The rod is connected to a butterfly valve, not shown, that
is
located in the air passageway between the port 47 and the associated inlet
port in
the carburetor. As will be understood by those skilled in the art, rotation of
the rod
70 in one direction causes the butterfly valve to open while rotation of the
rod 70 in
the other direction causes the butterfly valve to close. The choke lever 30
includes
a hook-like projection 32 that is disposed within the hole 71 in the arm 69 so
that
longitudinal movement of the choke lever 30 will cause the arm 69 to move
between
the positions shown in FIG. 5 and FIG. 6, respectively. In turn, this movement
of the
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arm causes rod 70 to rotate and that rotation will cause the butterfly valve
located in
the passageway between port 47 and the associated inlet port in the carburetor
to
open and close. FIG. 5 illustrates the arrangement that exists when the choke
lever
30 is in a forward position and the butterfly valve is open and FIG. 6
illustrates the
arrangement that exists when the choke lever has been pulled outwardly and is
in a
rearward position and the butterfly valve is closed. It will be understood to
those
skilled in the art that the nature of the mechanical connection between the
choke
lever and the valve that controls the air flow through the filter housing into
the
carburetor may vary and need not be of the type specifically described.
[0038] From the foregoing it can be seen that the choke lever 30 is
connected to an air valve for controlling the flow of air to the carburetor
and that the
lever is reciprocally movable between a first position, as shown in FIG. 5, in
which
air flow to the carburetor of the chain saw is not substantially restricted,
and a
second position as shown in Fig. 6, in which air flow to the carburetor is
substantially restricted. The choke lever also includes an abutment 33, the
purpose
of which is described below.
[0039] A butterfly valve is also located in the air flow path between port 46
in
the filter base and the corresponding inlet port in the carburetor. The
operation of
this valve, however, is independent of the choke mechanism and is controlled
by the
chain saw's throttle mechanism in a manner familiar to those skilled on the
art. It
should be noted that the operation of the chain saw does not require a second
air
inlet such as port 46 and a corresponding inlet port in the carburetor.
[0040] The ignition switch 29, which also forms a part of the ignition
assembly of the invention as has been described, is positioned on the mounting
element 58 so as to be movable between the "Off", or stopping, position in
which the
chain saw cannot be operated and the "On", or running, position in which the
chain
saw can be operated. In general, the arrangement of the ignition switch in the
stopping position is shown in FIG. 5 and the arrangement of the ignition
switch in
the running position is shown in FIG. 6. As can best be seen from these two
figures,
the ignition switch includes a depending abutment 23 that is located in the
line of
reciprocal movement of the depending abutment 33 of the choke lever when the
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ignition switch is in the stopping position so that reciprocal movement of the
choke
lever from its first position, when air flow to the carburetor is not
substantially
restricted, to its second position, when air flow to the carburetor is
substantially
restricted, causes the depending abutment 33 on the choke lever to engage the
depending abutment 23 on the ignition switch and pivotally move the ignition
switch
on the mounting element 58 from the stopping position to the running position.
It
should be understood that it is not required that the ignition switch be
mounted for
pivotal movement on a mounting element that is integral with the air filter
housing,
and the ignition switch can be variously mounted to a mounting element in the
chain
saw or other power tool, the important consideration being that the choke
lever
moves the ignition switch from the "Off' position to the "On" position when
the choke
lever moves from its first position to its second position.
[0041] The ignition assembly also includes the S-shaped leaf spring which,
as described above, is held in place on the filter housing at its intermediate
section
65. The first terminal section 66 of the leaf spring includes a rounded
protuberance
72 that engages the ignition switch at a first site of engagement 24 on the
ignition
switch when the ignition switch is in the "Off' position and engages the
ignition
switch at a second site of engagement 25 on the ignition switch when the
ignition
switch is in the "On" position. As can be seen, in particular from FIGS. 5 and
6 of
the drawings, the S-shaped leaf spring is biased for alternatively applying a
force to
the ignition switch at the first and second sites of engagement in a direction
toward
the mounting element 58 and away from the choke lever 30. It will be
understood
that the leaf spring need not be S-shaped or include a rounded protuberance
and
other arrangements can be employed so that a force on the ignition switch
directed
toward the mounting element is provided and so that engagement by that force
is
made at two engagement sites on the ignition switch.
[0042] As shown in the embodiment of the invention illustrated in the
drawings, the leaf spring forms a part of the ignition circuit described above
and the
continuity of the ignition circuit is established when the first terminal
section 66 of
the leaf spring engages the ignition switch at the first site of engagement
and the
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continuity of the ignition switch is interrupted when the first terminal
section 66 of the
leaf spring engages the ignition switch at the second site of engagement. This
is
accomplished in the embodiment of the invention illustrated in the figures by
the
connection 74 between the second terminal section 66A of the leaf spring and
the
ignition circuit, on the one hand, and the connection between the electrical
conductor 26, in the shape of an annulus, that is located at the first site of
engagement 24 on the ignition switch 29 and the ignition circuit on the other
hand.
The ignition switch 29 includes an opening 27 that extends through the
ignition
switch, and the annular conductor 26 is press-fitted into the opening 27. The
ignition switch also has positioning means 28 that are located adjacent
opening 27
for maintaining the electrical conductor 26 in place on the ignition switch
29.
[0043] From the foregoing description it will be understood that the present
invention will function in conjunction with a portable chain saw as follows:
Initially,
the ignition switch 29 will be in the "Off' position and the chain saw will be
in the
non-operational mode. At the same time, the choke lever 30 will be in a
forward
position. This state of affairs is best seen in Fig. 5. As shown in Fig. 5,
the rounded
protuberance 72 of the S-shaped leaf spring will be engaging the ignition
switch at
the first site of engagement 24 on the ignition switch and will be in contact
with
conductor 26. Under these circumstances, the coninuity of the chain saw's
ignition
circuit will be established and the ignition module in the ignition circuit
will be
grounded. As a result, the ignition module will not provide current pulses to
the
spark plug. When it is desired to start and operate the chain saw, and
conditions
are such that a fuel-rich air-fuel mixture is required, the choke level 30 is
pulled
outwardly of the chain saw in the direction of the arrow in Fig. 6 thereby
rotating arm
68 in the direction of the arrow in Fig. 6 and causing rod 70 to actuate the
butterfly
valve located between port 47 in the air filter housing base and the air inlet
in the
carburetor and, substantially, close the valve. As that occurs, the abutment
33 on
the choke lever, by engaging the abutment 23 on the ignition switch, will
cause the
ignition switch to pivot about mounting element 58 in the direction of the
arrow in
Fig. 6. As a result, the rounded protuberance 72 on the first terminal section
66 of
the S-shaped leaf spring, because the leaf spring is biased so as to provide
an
14
CA 02496056 2005-02-04
upward force to the ignition switch toward the mounting element, will engage
the
second engagement site 25 on the ignition switch. This arrangement is
illustrated in
Fig. 6. At this point, the protuberance 72, and consequently the S-shaped leaf
spring, will be out of contact with conductor 26 and the continuity of the
ignition
circuit will be interrupted. Therefore, the ignition module will no longer be
grounded
so that the ignition module will be able to provide current pulses to the
spark plug
causing the spark plug to emit sparks that will ignite the air-fuel mixture in
the
engine and place the chain saw in an operating mode. As the engine begins to
run,
the choke lever can be adjusted to any position required for the engine to
finally
attain its optimum operating speed without affecting the position of the
ignition
switch. Normally, the choke lever will be returned to its inward-most location
which
coincides with the butterfly valve being positioned so as to permit the
substantially
unrestricted flow of air to pass through the filter housing to the carburetor.
[0044) While a presently preferred embodiment of the invention has been
shown and described herein, it is to be understood that the invention is not
so
limited but covers and includes any and all modifications and variations that
are
encompassed by the following claims.
